Identity Stitching
On this page, <package> can be one of: web, mobile
Identity stitching is the process of taking various user identifiers and combining them into a single user identifier, to better identify and track users throughout their journey on your site/app.
The web and mobile packages contains a User Mapping module that aims to link user identifiers, namely domain_userid/device_user_id to user_id. The logic is to take the latest user_id per domain_userid/device_user_id.
The domain_userid/device_user_id is cookie/device based and therefore expires/changes over time, where as user_id is typically populated when a user logs in with your own internal identifier (dependent on your tracking implementation). If you do not currently set a user_id as part of your tracking for logged-in users, we recommend that you begin doing this as without some assigned ID it is not possible to stitch domain_userid together.
This mapping is applied to the sessions table by a post-hook which updates the stitched_user_id column with the latest mapping. If no mapping is present, the default value for stitched_user_id is the domain_userid/device_user_id. This process is known as session stitching, and effectively allows you to attribute logged-in and non-logged-in sessions back to a single user.
If required, this update operation can be disabled by setting in your dbt_project.yml file (selecting one of web/mobile, or both, as appropriate):
vars:
snowplow_<package>:
snowplow__session_stitching: false
In the web package, since version 0.16.0, it is also possible to stitch onto the page views table by setting the value of snowplow__page_view_stitching to true. It may be enough to apply this with less frequency than on sessions to keep costs down, by only enabling this at runtime (on the command line) on only some of the runs.
User mapping is typically not a 'one size fits all' exercise. Depending on your tracking implementation, business needs and desired level of sophistication you may want to write bespoke logic. Please refer to this blog post for ideas. In addition, the web package offers the possibility to change what field is used as your stitched user id, so instead of user_id you can use any field you wish (note that it will still be called user_id in your mapping table), and by taking advantage of the custom sessionization and users you can also change the field used as the domain_user_id. We plan to add support for these features to the mobile package in the future.